Heat dissipation concerns are on an increase in recent years, following the clustering or closer placement of components on circuit boards. Due to the proximity of these parts, it has become increasingly difficult to dissipate or keep away heat or thermal energy within the board. Today, one can use thermal relief pads to conduct heat away from the components.
In this article, we define thermal relief PCB, explain the important and explain how you can maximize it for the best thermal management results.
Thermal Relief PCB Meaning
Thermal relief, also called thermal relief pad and thermal pad, refers to the dedicated pad that manages heat/thermal transport in a circuit board.
Thermal Relief PCB Footprint
The primary function of the pad is to provide “relief” to the PCB, in terms of the heat conduction capabilities. For this purpose, let us look at some of the factors that go into making the footprint.
The Location
The thermal relief PCB pad is designed as a large area of metal, meant for enabling the soldering of the metal to either the circuit board or the device.
It is also possible to solder or attach the metal to other surfaces, such as heatsink and a bolt.
Thermal Relief PCB Connection
The pad is usually connected between the heatsink and the heat-generating components. This is done to facilitate the further conduction away of the heat coming from these parts. That way, other components wouldn’t be exposed to the heat and the negative effects.
Also, the thermal relief pad is commonly used in the location where there is either an existing connection between the fan-out via or the component pin to the copper plane.
The Copper Pour Connection
The argument is on whether the thermal relief pad is to be connected to the copper pour or to the tracks. These tips will help you make the right thermal relief PCB connections:
- The thermal relief pad can be connected to the copper pour via a thermal connection. The connection is enabled by the use of 3 to 4 traces of copper spokes to have the pad attached to the surrounding copper.
- For the best results, it is best to connect the pad to a few narrow tracks. The reason is that a direct connection to the copper pour makes the pad’s soldering difficult.
PCB Thermal Relief Guidelines
Designers ought to follow certain steps and guidelines, as these help them optimize the thermal relief pad for the best results.
Here are the cardinal points of utilizing the pad in your circuit board’s layout:
Thru-Hole Component Pins
Also called the thru-hole pins; these are the pins, which have been drilled through the circuit board for soldering purposes. The major concerns for using the thermal relief PCB pad for these pins are:
Cold Solder Joint
There is a risk of having a cold solder joint created. It is a result of the inability of the thru-hole pins from getting enough heat for solderability purposes.
The reasons for the inability to create good solder joints include:
- The tendency of having heat pulled away from the pin by a split plane or any other small metal area. The resultant effect is that the area serves as a heatsink and takes away the heat.
- The cold solder joints are created in multilayered PCBs, whereby an excessive amount of heat is required to extend beyond the several square feet of metal.
Forceful Heat Application
There is another risk of having heat forcefully applied towards the melting of the solder. This happens as a result of trying to “unsolder” the solder that was directly soldered to the larger areas of the metal.
The outcome of doing this is that the surrounding components/parts and traces are exposed to damages.
Surface Mount Pins
These are pins used for Surface Mount Devices (SMDs). Possible issues tend to arise with the smaller, two-pinned SMT devices. These problems arise due to the directly soldering of one of the pins to the larger area of metal.
Here are some of the reasons why PCB designers would embed a surface mount pad in a metal fill:
- The embedding might give the best of electrical performance, but it comes at the expense of pulling away heat from the thermal relief pad.
- There is also a risk of having one side of the solder melting faster than the other, due to the imbalance of the metal between the pins.
The best way to tackle the imbalance of the metal is to use several traces to connect a surface mount thermal relief pad. This proves to be a better option, rather than having it embedded into the large area of metal.
Metal Routing
There is a tendency that the metal wouldn’t be enough to enable the connection of the spokes to the surrounding copper. This happens due to the following reasons:
- The automated process of using CAD systems for adding the thermal relief PCB pads to the pins often impacts the pad. This also leads to limited space for the spoke-to-copper connection.
- Certain power traces with lower conducting levels of current are often routed with the narrower traces.
Vias
There might be no need to use the thermal relief PCB with the vias, especially the ones that connect to the larger area fills, power planes and ground planes. The reason is that they don’t often have pins soldered into them.
The primary consideration for using the pad for the vias is due to the following reasons:
- If you are using nets that conduct higher current levels.
- If this is the case, use the thermal relief PCB pad because some short power traces might facilitate excessive heat conduction to the surface-mount pins.
What is the Purpose of Thermal Relief in PCB?
You need to know when to use thermal relief PCB for your circuit board. The following are some of the benefits:
- The pads aid in the manufacturability of circuit boards.
- You can use thermal relief PCB pads to provide a robust electrical connection from the pad to the plane.
- It also aids in the preventing of excessive heat dissipation into the metal plane.
Conclusion
Thermal relief pads are used in PCBs to bolster the restriction of heat flow into the copper pour, keeps the heat confined in the pad required for PCB component mounting and improving the pad’s solderability.
